Method of making apparatus for sensing temperature

ABSTRACT

Measuring the surface temperature of a wall heated by a flowing fluid without disturbing the boundary layer. A thin electrical conductor forming a thermocouple junction is covered by a layer of protective material to guide the flow of fluid over the junction.

[ Oct. 24, 1972 [56] References Cited UNITED STATES PATENTS [54] METHODOF MAKING APPARATUS FOR SENSING TEMPERATURE [72] Inventor: Ronald G.Huff, North Olmsted,

Ohio

[73] Assignee: The United States of America as Baum et 1 36/2303,488,839 1/1970 Proxmire.................29/628 x E' by Administm3,553,827 1/1971 Baker et al...............29/628 x the NationalAeronautics and Space Administration May 26, 1971 21 Appl. No.: 147,099

Primary Examiner-John F. Campbell Assistant Examiner-Richard BernardLazarus [22] Filed:

AttorneyN. T. Musial, G. E. Shook and .I. R. Manning Related [1.8.Application Data [62] Division of Ser. No. 877,717, Nov. 18, 1969,

[ ABSTRACT Measuring the surface temperature of a wall heated by aflowing fluid without disturbing the boundary layer, A thin electricalconductor forming a thermocouple Pat. No. 3,671,329.

[52] US. Cl. .......................29/573, 29/624, 136/233 [51] f 17/0015/001 49/00 junction is covered by a layer of protective material to[58] Field of Search............29/l57 R, 624, 628, 573; guide the flowof fluid Over the junction 10 Claims, 3 Drawing Figures P'A'TENTEU 0m 24m2 INVENTOR RONALD G. HUFF ATTORNEYS METHOD OF MAKING APPARATUS FORSENSING TEMPERATURE STATEMENT OF COPENDENCY This application is adivision of application Ser. No. 877,717 which was filed Nov. 18, 1969,now US. Pat. No. 3,671,329.

STATEMENT OF GOVERNMENT OWNERSHIP The invention described herein wasmade by an employee of the United States Government and may bemanufactured and used by or for the Government for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to the measurement ofwall temperatures in regeneratively cooled rocket engines having thinwalled cooling passages. The invention is particularly concerned withmaking an improved thermocouple device for sensing the temperature onthe hot side of a thin-walled cooling passage.

As rocketry advances there is a need for better heat transferinformation. A problem encountered in obtaining such information inregeneratively cooled engine's has been in the measuring of thehot-gas-side wall temperatures. It is this temperature which plays avery important part in determining the burn out condition in aregeneratively cooled rocket engine, and its measurement is vital incorrelating data used to design high pressure-heat flux engines.

One of the reasons why this measurement is so difficult is that thethickness of the cooling tubes is about 0.01 inch. It has been proposedthat thermocouples be attached directly to the surfaces of these tubes.Thermal conduction and the disturbance of the fluid stream change thetemperatures at the thermocouples.

Optical pyrometers are used in other studies where the surfaces can beseen. However, the radiation from the burning fluid obscures the surfaceof the rocket engine, and the use of such pyrometers is not practical.

SUMMARY OF THE INVENTION These problems have been solved in a systemconstructed in accordance with the invention. A very fine wire having aquartz jacket with an outside diameter of less than 0.003 inch is usedas one leg of a thermocouple. This wire is bent to the contour of acurved wall. A portion of the jacket is removed from one end to providea small length of exposed wire which is then attached to the surface ofthe wall. A cover layer is formed by electroplating a layer of metalover the wire to protect the junction from hot gases. The walltemperature is determined by reading the voltage generated by thethermocouple junction formed by the wire and the material from which thewall is fabricated.

OBJECTS OF THE INVENTION It is, therefore, an object of the presentinvention to make a thermocouple which can measure wall temperatureswithout disturbing an adjacent boundary layer.

Another object of the invention is to provide a method of making athermocouple junction on the hot side of a wall having hot gases flowingover the surface.

A further object of the invention is to provide a method of making animproved thermocouple device utilizing a single conductor and junctionwhich minimizes conduction to give a more accurate temperature reading.

These and other objects and advantages of the invention will be apparentfrom the specification which follows and from the drawings wherein likenumerals are used throughout to identify like parts.

DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view of arocket engine' having thermocouples mounted in accordance with theinvention.

FIG. 2 is an enlarged perspective view of a portion of theregeneratively cooled rocket engine shown in FIG. 1.

FIG. 3 is an enlarged sectional view taken along the line 3-3 in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings atypical rocket engine 10 in the form of an annular hollow elongatedenclosure is shown in FIG. 1. The rocket engine 10 includes an upstreamcylindrical combustion chamber 12, an adjacent downstreamconvergent-divergent throat section 14, and an exhaust nozzle 16. Hotgases from the combustion chamber 12 pass through the throat section 14to the nozzle 16 in a manner well known in the art.

The enclosure that forms the casing for the rocket engine 10 is formedby a number of contiguous tubes 18 connected together by brazingmaterial 20 or the like as shown in FIG. 2. A fluid flows through thetubes 18 to regeneratively cool the rocket engine 10 in a conventionalmanner. Stainless steel tubes 18 having thin walls on the order of 0.01inch in thickness are utilized in high heat flux engines. With such thintubes knowledge of the true temperature on the hot-gas-side wall insidethe engine 10 is extremely important for proper design.

These temperatures are obtained by thermocouples 22, 24 and 26 that areconstructed in accordance with the present invention. The thermocouplesare mounted on the side of the tubes 18 adjacent the hot gases flowingfrom the combustion chamber 12 to the nozzle 16. Although the inventionis shown and described with respect to its application to regenerativelycooled rocket engines, it may be employed to any type of thin wall whereaccurate temperature measurement is required.

According to the invention one leg of each thermocouple 22, 24 and 26 isformed by an electrical conductor 28 covered with insulation 30. In thepreferred embodiment the insulation 30 is in the form of a quartzcovering about a small wire 28. The outside diameter of the wireincluding the quartz insulator is less than 0.003 inch. The wire 28 hasa diameter less than 0.001 inch. These small dimensions may be achievedby hot drawing the wire and the quartz simultaneously.

A portion of the insulating material 30 is removed from the end of thewire 28 as shown in FIG. 3. The exposed end of the wire 28 is spotwelded at 32 to the outer wall of the coolant passage 18. The insulatedwire 28 and spot welded end 32 are then covered by a metal layer 34 aswill be explained later in detail.

A thermocouple junction comprising two secondary junctions is formed.One junction exists at the point where the wire 28 enters the quartz 30.The other junction is located at a point on the metal layer wallinterface adjacent the first junction.

The stainless steel wall forms the other leg of each thermocouple. Alead wire 33 is attached to the outwardly facing wall of the tube 18 asshown in FIGS. 1 and 3. It will be appreciated that the spot welding ofthe wire 28 to the tube 18 merely facilitates assembly in thisembodiment.

The layer of metal 34 forms a protective covering over the wire andjunction. The metal layer 34 is electroplated on the surfaces of thetubes 18 adjacent the thermocouples 22, 24 and 26. The metal 34 is anymaterial which may be electroplated, such as copper or nickel. Theplating thickness is on the order of 0.005 to 0.009 inch.

An important feature of the invention is that the marginal peripheraledges of the plated metal 34 are faired as shown in FIGS. 2 and 3. Thiseliminates disturbances to the boundary layer between the hot flowinggases and the wall.

Each of the thermocouples 22, 24 and 26 is constructed in the mannerpreviously described. Referring to FIG. 3 thermocouple 26 is provided atthe crest of the tube 18. Thermocouple 24 is provided at a point whichis 45 from the crest. Thermocouple 22 is mounted at the braze line ofthe tube 18.

Providing thermocouples of such fine diameter wire creates certainmanufacturing problems. These have been overcome by the installationprocedures of the present invention. The area where the junction 32 isto be provided is thoroughly cleaned prior to attaching thethermocouple. This cleaning may be accomplished by filing. The areawhich is to be covered by the electroplated metal 34 shown in FIG. 2 isthen masked by painting the surrounding area with acid resistant paint.

An insulated wire is bent to the desired diameter to fit the tube 18.This is accomplished by directing a torch into the end of a ceramic tubehaving the same diameter as the rocket cooling tube 18. The ceramic tubeis heated to about 2,365 P. The quartz jacketed wire is laid on the tubeand gently bent to the desired shape.

The end portion of the quartz jacket is removed from the wire afterbending by etching with hydrofluoric acid. The quartz also may beremoved by cracking the end portion and sliding the quartz from thewire.

An access hole 36 is provided between the engine cooling tubes 18 duringthe engine brazing process by placing stop off material between thetubes. The stop off is removed after the brazing has been completed. Inan alternate process lengths of quartz tubing are inserted between thetubes 18 before brazing and removed by etching with hydrofluoric acidafter brazmg.

The performed quartz insulated thermocouple wire 28 is passed throughthe access hole from inside the engine 10. The wire 28 is positionedwith the aid of an optical assembly. The end portion of the wire is thenspot welded to the cooling tube 18. A capacitance-discharge t ewelderhas been satisfacto f0 th' eights as are attached to the Jii t fi ld thepreformed thermocouple close to the cooling tube 18 during planting. Ifthe quartz insulator moves away from the surface of the tube 18, themetal 34 will not cover the thermocouple assembly. Also the quartzinsulator 30 may be covered at the crest and locked in place while theremainder of the quartz is allowed to move. This would result inbreakage of the quartz and would allow the plated metal to short thethermocouple causing a secondary junction.

What is claimed is:

l. A method of making a thermocouple on the hot side of a wall havinghot gases flowing thereover comprising the steps of cleaning the surfaceof the wall where the thermocouple is to be located,

masking a portion of the wall around the cleaned surface,

bending a wire having an insulating cover to the contour of the wallsurface,

removing the insulating cover from an extreme outermost end portion ofsaid wire,

securing the exposed end of the wire to the cleaned surface of the wall,and

electroplating a layer of metal over said covered wire in the unmaskedportion of the wall.

2. A method of making a thermocouple as claimed in claim 1 including thestep of hot drawing the wire and insulating material simultaneouslyprior to bending to the contour of the wall surface.

3. A method of making a thermocouple as claimed in claim 2 including thestep of hot drawing the wire and insulating material to an outsidediameter of less than about 0.003 inch.

4. A method of making a thermocouple as claimed in claim 3 including thestep of hot drawing the wire to a diameter of less than about 0.001inch.

5. A method of making a thermocouple as claimed in claim 3 including thestep of hot drawing quartz insulating material.

6. A method of making a thermocouple as claimed in claim 1 including thestep of spot welding the exposed end of the wire to the cleaned surfaceof the wall.

7. A method of making a thermocouple as claimed in claim 1 including thestep of electroplating a layer of metal over the covered wire in theunmasked portion of the wall to a thickness from about 0.005 inch toabout 0.009 inch.

8. A method of making a thermocouple as claimed in claim 7 including thestep of electroplating a layer of metal selected from the groupconsisting of copper and nickel.

9. A method of making a thermocouple as claimed in claim 7 including thestep of fairing the marginal peripheral edges of the layer of platedmetal.

10. A method of making a thermocouple as claimed in claim 1 includingthe step of bending the wire having an insulated cover over a heatedceramic tube having the contour of the wall surface.

2. A method of making a thermocouple as claimed in claim 1 including thestep of hot drawing the wire and insulating material simultaneouslyprior to bending to the contour of the wall surface.
 3. A method ofmaking a thermocouple as claimed in claim 2 including the step of hotdrawing the wire and insulating material to an outside diameter of lessthan about 0.003 inch.
 4. A method of making a thermocouple as claimedin claim 3 including the step of hot drawing the wire to a diameter ofless than about 0.001 inch.
 5. A method of making a thermocouple asclaimed in claim 3 including the step of hot drawing quartz insulatIngmaterial.
 6. A method of making a thermocouple as claimed in claim 1including the step of spot welding the exposed end of the wire to thecleaned surface of the wall.
 7. A method of making a thermocouple asclaimed in claim 1 including the step of electroplating a layer of metalover the covered wire in the unmasked portion of the wall to a thicknessfrom about 0.005 inch to about 0.009 inch.
 8. A method of making athermocouple as claimed in claim 7 including the step of electroplatinga layer of metal selected from the group consisting of copper andnickel.
 9. A method of making a thermocouple as claimed in claim 7including the step of fairing the marginal peripheral edges of the layerof plated metal.
 10. A method of making a thermocouple as claimed inclaim 1 including the step of bending the wire having an insulated coverover a heated ceramic tube having the contour of the wall surface.